The invention, in some embodiments, relates to methods and devices for imparting distance information to a human subject, especially a visually-impaired human subject.
The invention, in some embodiments, relates to the field of assistance for the visually-impaired, and more particularly, in some embodiments, to methods and devices for imparting distance information to a visually-impaired human subject.
Visual perception enables humans to be aware of surrounding objects, to navigate and to interact with the world.
Blindness is the condition of lacking visual perception due to physiological or neurological factors. Total blindness involves complete loss of perception of form and visual light. In North America and most of Europe legal blindness is defined as visual acuity of 20/200 (6/60) or less in the better eye with best correction possible. Approximately ten percent of those deemed legally blind are totally blind, the rest having anything from minimal light perception to relatively good acuity.
Visually-impaired, including totally blind, people require methods and tools that allow completion of daily activities using the remaining senses. Such tools include the white cane which is used to extend the range of a user's touch to about 100 to 150 cm to allow independent locomotion.
For use, the white cane is usually swung in a low sweeping motion across an intended path of travel to detect physical features that may constitute an obstacle including upwardly projecting features such as stairs and poles and downwardly projecting features such as curbs and holes.
The white cane is invasive: to detect an object, the white cane must contact the object which may not be convenient when the object is fragile, moving or is a living being. The white cane requires that the user walk close to a curb or a wall which may be inconvenient or undesirable. The white cane allows detection of the presence of an object within the reach of the cane but gives no other information about the surroundings. Suspended obstacles are not easily detectable. The white cane provides little information regarding the appearance (e.g., size and shape) of an object.
A “virtual” white cane has been disclosed by Yuan D and Manduchi R (Dept. Comp. Eng., U. California, Santa Cruz, USA, described in Proceedings of the 2004 and the Proceedings of the 2005 IEEE Computer Society Conference on Computer Vision and Pattern Recognition). The Yuan and Manduchi virtual white cane collects range information by a short-baseline triangulation system formed by a point laser (2 mrad nominal divergence) and a miniature camera (1024×768 CCD pixels). Specifically, a user scans the environment by swinging the device around a horizontal axis (up and down) at a constant rate and acquires instantaneous range information at the camera frame rate (15 Hz). At least two succeeding frames are used to determine a range which is then used to identify discontinuous environmental features critical for mobility such as curbs, steps and drop-offs. Specifically, the time profile of determined ranges is analysed by an on-board processor implementing an extended Kalman filter to identify a discontinuous feature. Information about detected environmental features is imparted to the user with special haptic primitives such as small jolts, that are likely to be unpleasant, especially when repeated, such as when scanning a flight of stairs.
The device, though purportedly hand-held, is ungainly, comprising a round handle with a diameter of about 4 cm to which distal end is secured a component housing about 10 cm deep, 15 cm high and 30 cm wide. In the above-referenced documents is reported that the distance between the camera and laser aperture is 8 cm, although from a photograph (2005 document) it is seen that the distance is far greater. The device does not provide instantaneous distance information, but only information about the presence of large discontinuities, on the order of 27 cm. The device is difficult to use, working only when scanned at an impractically slow and preferably constant rate of 7°/sec.
In addition to the two articles authored by Yuan and Manduchi referenced above, devices and methods known in the art that provide a background for understanding the teachings herein are described in U.S. Pat. No. 5,487,669.